For formation of a small-size via-hole of 100 μm or less on copper clad laminates in recent years, laser drilling is mainly used. To enhance the laser drilling performance, a method which carry out the so-called “black-oxide treatment” on the laser drilled sites of copper clad laminates and/or printed wiring boards to improve absorption of laser beam has been employed.
For example, Patent document 1 discloses the method including the steps; the step of subjecting a metal foil to a black-oxide treatment to provide a black-oxide film, the step of laminating the metal foil to an insulating substrate wherein the black-oxide film faces to bottom portions of the insulating substrate where via-holes are formed, the step of irradiating the laser beam on the insulating substrate to form via-holes having the metal foil as bottom parts, the step of subjecting a desmear treatment on the metal foil exposed at the bottom of via-holes, the step of carrying out soft etching on the metal foil exposed at the bottom of via-holes, the step of confirming that the soft etching leaves no black-oxide film on the metal foil surface at the bottom of via-holes, the step of forming a plated metal film inside the via-holes and the step of etching the metal foil to form a conductor pattern, to provide a printed wiring board having a high conductive reliability in via-holes and a manufacturing method.
As an invention using a black-oxide treated surface in the laser drilling, Patent document 2 discloses the method using a copper clad laminate which satisfies the conditions of a laser beam reflectance of 86% or lower and a luminosity (value L) of 22 or lower by forming fine copper oxide or fine copper particles on the surface of an outer layer copper foil of a copper clad laminate to provide a copper clad laminate suitable for formation of a through-hole and/or a blind-hole as through holes or via-holes for interlayer connection among copper foil circuit layers and an outer layer copper foil by using a laser method.